Process of separating hydrocyanic acid



and the like, contain, also phuretted hydrogen and ammonia.

ammonium-sulphocyanate, the

'phide than is requisite 7 acid, the excess thereof is'oxidized to ammonium- Patented July 16, 1935 UNITED STATES mowi- PRocEss ,oF siirARAmiNl' nnbitooxiamc Aom' 1 Walter Klempt, Dortmund-Ewing, Germany, as-

signor to Beschrankter Haftung, Dortmund-Ew ng, 'Germany No Drawing. Application Mayjil, 1932,1Serial No.

610,747. InfGermanV'MayfZS,193i

, 7 Claims. -(Cl. 2341c) F This invention relates to an improved process of separating hydrocyanic acid from such-industrial gases which, like lighting gas, coke oven gas, besides hydrocya-nic. acid,

The hydrocyanic acid has up to now been removed from said gases by washing these latter Withan aqueous suspension of finely distributed free sulphur, but thatprccess necessitates the employrnent of very finely ground sulphur of a foreign origin, at least free sulphur, which first must be produced by means of i a particular method.-=

I have discovered that the employment of 'sp'e' cially manufactured sulphur for thepurpose of re moving hydrocyanic acid from gasescan be 'dispensed with if, in order to convert this acid into sulphuretted-hydrogen itself contained in the respective gases is used. If sulphide of nickel or another suitable nickel salt by which sulphide of nickel is precipitated owing to the action of the ammoniaa'nd the sulphuretted hydrogen, is admixed to thewashing liquid free sulphur is disengaged from the sulphide of nickel under the oxidizing influence of the oxygen likewise containedin the respective gases, but the thus formed hydroxide of nickel is at once again converted into sulphide of nickel by the further supply of sulphuretted hydrogen whereby again sulphur is separated, and soon. The thus formed free sulphur reacts with the sulphide of ammonia contained in the liquid where'- by ammonium poly-sulphide is formed which takes up the hydrocyanic acid contained in the gases whereby ammonium-sulphocyanate is formed. If there is more ammonium-polysizlto take up the hydrocyanic thiosulphate which contaminates the rhodammonium lye formed and renders the-working of the same diflicult.

The behaviour of the substances mentioned can,

however, be influenced in such a'manner thatex-v clusively thiocyanate is formed if the amount not the nickel salt admixed to the washing llquidsis accommodated to the contents of oxygen in the respective gas about as follows: Withconsideration of the usual contents of oxygen of from,0.5 to 0.7 percent by volume for instance in coke oven gases the contents of nickel in the washing liquid should not be materially higher than from 0.5.

to 1 gram of nickel per 1 liter of the. washing liquid, if the separation of more sulphur than'is requisite for the formation of jammonium thio cyanate and, thus, also the formationof'ammoni um-thiosulphate, shall be prevented. *On the other hand, if 'thegas containsffrom 2'to2L51per- "Cent'by 'volum'e of oxygen, the contentsof nickel in' the washing liquid'should not bema'terially higher than from complete removal of the hydrocyanic acid shall be achieved without the disadvantage of the formation of .an =undesired excess of sulphur.

Whencarry ing 'ou'tithe process according to the "011 156013 gram per 1 liter, if

present invention, itis suited to the purpose to use a little lessn'ic'kel than is requisite for obtaining quantitative removal of the -hydrocyanic acid.

,On'e is wthenfsure that no soluble sulphur compounds; especially ammonium-thiosulphate, arise in thesolution. The rest ofithe hydrocyanic acid till coptamesin the gases can be reliably re-.

movedlfromlthem by Ladding a slight amount of finely pulverized sulphur to the washing liquid.

In order to make matters still moreclear I point out what follows: The presentinvention relates to the practically complete removal of hydrocyanic acid from coal -.distillationlgases, but my improved process does not aim' alsoI 'atfthe complete removal of the sulphuretted hydrogen also contained in the respective gasesl Swing thereto, only so much sulphurettedhydi'ogen' is removed from the gases as is 'requisite to, convert the cyanogen radical, 'CN, into thiocyanogen radical, CNS. The excess of the sulphure'tted hydrogen is removed by anotherway which does not form a part of the present invention.

In carrying out my improvedprocess, I make use fo'fflsuc'h anlamount-lof nickel that only a part of thelsulphuretted hydrogen-is washed o'utin the form olsulphide of nickel, and another part thereof forms, sulphide of ammonia with the a monia present in the gas. This sulphide of amr'noniafformsf'together. with the sulphur separa'tef'the sulphur reacting with the existing ammonium sulphide and forming poly-sulphide. There ls't'hus, under "this condition, more polysulphide formed'th'an is requisite for converting the 'cyanogenradical,,*CN; into thiocyanogen radloa1,"'jCNS, so that now the oxygen or the gases has'an opportunity-to "oxidize the excess of ammoniumpolysulphide to ammonium-thiosulphate'. If theam'oun'to'f nickel contained in the eration was composed as follows: 25 v washing lye is fixed already from the beginning, then the same disadvantage will be experienced if from any reason during the service the content of oxygen in the coke oven gases increases. If, for instance, at a certain definite contents w of hydrocyanic acid, and simultaneously therewith at a content'of oxygen of 0.4% by volume a content of 0.05% by ,volume of nickel in the washing liquid has been found to be proper for forming only so much poly-subphide as is requisite for converting the hydrocyanic acid into thiohydrocyanic acid, then that content of nickel is no longer suited for the purpose inview if the content of oxygen in the 'gases amounts to more than 0.4% by volume. In this case the excess of ammonium-polysulphide formed is in'the position to form,;be sides ammonium-thiocyanate, also ammonium-thiosulphate, and this be the more the case, the more the content'of oxygen in the gas increases. 7

The effect of my improved process will now be shown with" the aid of the following examples:

A coke oven gas subjected to the washing op- From 10.5 to 11.5 g/cbm of H28 from 1 to 1.2 'g/cbm of HCN 6 g/cbm of NH3 I 2.1'g/cbm of CO2 from 0.8'to1 .2 /Cbm of O2.

Every hour 2 cbm of'thisgas were Washed in a small iron vessel filled with grid-work. The washing lye was set in circulationby means of a cog-wheel pump with a speed of about from 6 to 8 liters per hour and was distributed over the gridwork' by means of a spray. In three tests 1000 cm of the washing liquid contained:

In the first case: V 11.5 grams'of N113 and 35 grams of S V In the second case: r V 11.5 grams of NI-Iaand 2.5 grams of Ni in the form of Ni(OI-I)2 1 In the third case: 11.5 grams of N133 and 0.75

form of Ni(OI-1) z. Inthe first case 35 grams of S were added after 20 ohm of gas had been led throughsaid vessel. Computed relatively to the amount of sulphocyanate formed until the end of the test 10%: of sulphur in excess had been employed.

The amount of hydrocyanic acid removed from gram of Ni in the the coke oven gas in all tests amounted in'average to from 98.9%

to of the HCN contained in the gas so that only from "0 to 0.011 gram of this acid could be ascertained in the purified gas.

After 50 cbm of gas had been led through the washing liquid contained in said vessel, there were ascertained in the washing liquids:

" In the first case:

14.9% of ammonium rhodanide (:53 g. of HCN) and 1.2%ofthiosulphate.

Inthe second case: i 15.2% of ammonium rhodanide (=54 g. of HCN) and 9.8% of thiosulphate. In the third case: I I r i 14.7% of ammonium rhodanide (=,52,2 g. of HCN) and 1.3% of thiosulphate." 1 f I While, thus, as regards the washing-out of hy-' drocyanic acid, the three testsshowed no differences, great differences were found when the washing liquid was examined with respect to-the undesired contents of thiosulphate. Considering the comparatively high percentageof oxygen in the gas very much thiosulphateis obtained when the equation 1 7 oxygen The content as regards the other components was practically the same as in the abovementioned three cases, and the tests were carried out in the same manner.

In the fourth case the washing liquid contained 11.5 grams of Ni in the form of Ni(OH) in 10 00 com. The hydrocyanic acid removed from the gas amounted to from 96 to 100% of the total amount contained in the raw gas. After 50 ohm. of gas had been led through the washing liquid,

this latter contained 14.3% of ammonium-mm danide (=50.7 grams of HCN) and 1.4% of ammonium-thiosulphate; This shows that if the percentage of oxygen in the gas is only small a percentage of the same magnitude as in the second of the three cases at first dealt with (2.5 grams of nickel in the form of Ni(OH)2 in 1000 com.) causes only a slight formation of thiosulphate.

v In the fifth case also a gas poor in oxygen was used. The percentage of nickel amounted only to 0.55 gram in 1 liter, also in the form of Ni(OH) 2, approximately corresponding to the third case.

The washing liquid contained 11.5 grams of NPR and 0.55 gram of Ni in the form of Ni(OH)i in 1000 com. After 50 ohm. of gas had been led through the liquid this latter contained 10.4% of ammonium rhodanide (:37 grams of HCN) and 0.4% of thiosulphate. The washing-out of hydrocyanic acid amounted only to from 65 to 78%. It was found that the contents of 0.55 g. of

nickel in 1 liter of liquid is not sufiicient for the complete washing-out of the hydrocyanic acid if the percentage of the oxygen in the gas is so slight as stated. The formation of thiosulphate is in such a case, of course, particularly slight.

'By adding such a small amount of elementary Ysulphur that it was just sufiicient'to bind that portion of hydrocyanic acid which hadnot been washed-out, complete washing-out of the hydrocyanic acid was attained'also with a sixth test carriedout in a manner analogous to the fifth case. As the amount of the nickel to be added cannot be computed prior to carrying out the test,

in that it depends on a variety of circumstances, such as percentage of oxygen, of sulphuretted hydrogen, and of hydrocyanic acid in the gas, of

the amount of the washing solution and of the gas to be led through it, as well as on the temperature, the process must be started in this way 7 that one commences with the lowest addition of nickel to the washing liquid appearing admissible with respect to the percentage of oxygen of the gas, and thatthen the contents of nickel in .the solution is slowly increased until about' from 98 "to 100% of the hydrocyanic acid are being washed out; It will then be foundthat at the same time only so much sulphur is washed out of the gas asis' requisite for the conversion of the entire amount of -hydrocyanic acid into rhodaniumhydrogen and that the formation of thiosulphate "is withoutimportance. 1'

In the carrying out of my present improved process the oxygen contained in thegasesacts upon the sulphide of nickel precipitated by the sulphuretted hydrogen in this way according to riches in ineffective, nickel v its further working is rendered difiicult. If the' have been withdrawn that it is temporarily converted into Qnickelhydroxide which, however, is' instantaneously converted intosulphide of nickel byth'e sulphur etted hydrogen present, the nickel-hydroxide act ing as it were, catalytically for the oxidation of the sulphuretted hydrogen to disengage sulphur. In this? way the percentage of the ammoniumsulphocyanide contained in the washinglyejcan, while the lye is circulating, pe'inereaseqhup to 35% without any decrease of the wasmngieaeet during the removal of the hydrocyanicacid. I I have also discovered that if thepercentage of hydrocyanic acid in. coking gases is very high or if the washing is carried-out at an increased temperature, a partof the sulphide of nickel can be dissolved in the form of'a nickel cyan complex salt. As this dissolved nickel cannot take'part in z the conversion oi the hydrocyanic acidlinto th'io hydrocyanic acid;fas above described, in thatitis no more precipitated by the sulphuretted hydro gen,the degree of the washing-out decreases in such a case at once so that, in order. to re.-estab-' lish the proper proportion between theoxygen and the active nickel of the washing liquid 'fresh amounts of nickel in the fornrof sulphide of nickelor of a nickel compoundadapted to be pre-; cipitated by sulphuretted hydrogen must .beadded for rendering the washing process again quantitative. V

This method delivers, it is true,an ammoniumsulphocyanate of a satisfying concentration, suffers, however, from the drawback that it, en-

complex salts whereby re-obtainment of the nickel converted into the complex salt would be given up, the process would become expensive by reason of therequisite con- ,1 tinual supply of fresh amounts of nickel.

Now, according to my improved process, the re-obtainment of the nickel in a form suited for the removal of the hydrocyanic acid is rendered possible thereby that parts of the solution which during the service, or that the entire amount of the solution, after the readily concentrated ammonium-sulphocyanide solution has been removed, is stirred with sulphur prior to its being furtherworked. .In this way there forms in the solution which contains ammonia, as well as sulphuretted hydrogen, ammonium-polysulphide which decomposes the complex nickel cyan compound into sulphocyan, there being precipitated. black sulphide of nickel, and

, the cyan radical being converted into said. sul

phocyan. Such a decomposition ofthe nickel cyan complex salt can, I emphasize, be effected only by the ammonium-hydrosulphide of ammonia likewise present in the liquid. The sul- J, phide of nickel separated in any suitable manner is re-conducted to the washing plant.- 1 sulphide of nickel re-obtained from the solution presents the advantage over freshlyprecipitated sulphur that it can be dissolved in solutions treat:

. ed with gases containinghydrocyanic acid only with pretty great difliculty, that is to say, soluble nickel cyan complex salts cannot easily be formed, but nevertheless transmission of the oxygen present in the coke oven gases to the sulphuretted hydrogen of the respective gases can be effected quickly and productively. The sulphide of nickel regenerated in that manner remains longer suited for the transmission of the sulphur to the hydrocyanic acid than does ordinary freshly precipitated sulphide of nickel.

:It the-sammonium-sulphocyanate solution, in the. ease ota strong concentration. as; regards the sulphocyanate, should contain too little sulphide" of "ammonia to precipitate the nickel from .out, of the nickel. cyan complex compound; and

to 'efiect: the, intermediate formation ofj-polysulphideof ammonia, which mayeasily occur when operating at too; high a temperature, forjinstance 30 C .,-'with gases poor in NH: and Has it is a matter. of course that sulphurette-d hydrogen from any source, for instance in the form of rawcon- V densed. gas water, maybeadded to the liquor; or the; waste vapors of :the ammonia-water separators. or waste damp of saturators may be introduced, into. the liquid. In order to furnish the ammonium polysulphide requisiteior the vdecom- Instead of decomposing the thusformed-nickel cyan complex salts by treating them withv sulphur, or with polysulphide; respectively, in the manner described, this part .of the process may be carried out alsoin this-way that the formationof such nickel cyan, complex salts duringthe washing procedure is preventedalready from the begin: ning. Itis suited tothe purpose to eifect that during the service by reducing the washing tem perature. If, for instance, the coking: gas is washed under normal conditions at a tempera! ture of about. 30 Cl, itis possible to increase the concentration of the sulphide of ammonia by diminishing the temperature to 209 C.- in m ost cases this contrivance will already sufi ice to prevent the sulphide. of nickel frombeingdissolved, that is to say to prevent theformation of soluble nickel c yan complex compounds which can no more be precipitated by means of sulphideoi ammonium. f h

, If the percentage, of sulphuretted hydrogen containedin the gases to be dealt with is nottoo small, one. will succeed when proceeding in. the

just stated manner by again precipitating already dissolved nickel from the nickel cyan complex theiform of sulphide ofnickel as a complex salt, as sufficient ammonium-polysulphide is forming. There is, however, presupposed in this case that still sufiicient sulphide of the washing liquid. A sufiicient quantity of sulphide of nickel must be present at all events. If that is not the case, either the'la'cking amount of sulphide of nickel,or a nickel salt adapted to be precipitated by sulphide of ammonia, or am moniunr polysulphide; or (to form this substance) elementarysulphur, must be added in order to start the reaction by the sulphide-oi nickelpresent.- 7 #Another. method for the re-obtainment of the sulphide of nickel especially in the case that the coke oven gases or the like are poor in oxygen consists in treating the washing liquid with air prior to conducting it back into the washing vessel. The sulphide of nickel still present in the form of a suspension delivers in that case free sulphur which reacts with the existing sulphide of ammonia in forming ammonium-polysulphide, and so precipitates in the form of sulphide of nickel that part of the nickel which has been disnickelis suspended in solved as a complex salt. "The amount of air used to carry out this procedure must, however, .be

'only slight as it is. onlyrto replace that portion which the gases are lacking. Treating the washing liquid with air takesplace'preferably in an intermediate vessel provided for the circulation of the liquid. '11; is also possible to design the pipe leading to the upper part of the'washing vessel or tower in such a manner, that the liquid is treated with air while it flows through saidl'pipe'.

I claim:

The process of separating hydrocyanic acid in the form of ammonium thio-cyanateirom gases containing-said acid, ammonia, and sul- ;phuretted hydrogen with theaid of washing .lyescontaining nickle compounds, said process consisting in adding to the washing lye an amount of the nickel compounds sufiicient to produce the amount of ammonium-polysulphide requisite for the conversion of the'hydrocyanic'acid intoammonium-thiocyanate, and insufiicient to form soluble sulphur "compounds rendering the lye impure.

2. Theprocess of separating hydrocyanic acid in the form of ammonium thiocyanate "from gases containing said acid, ammonia, and sulphuretted hydrogen with the aid' of washing lyes containing nickel compounds, said process consisting in dissolving nickel cyanogen complex compounds, introducing ammonium 'polysulphide into the solution so as to precipitate thereby sulphide of nickel ontof said solution of the nickel cyanogen complex compounds,and introducing into the washing lye already at the commencement of the washing operation an amount of said sulphide of nickel sufiic'ientto produce the amount of ammonium-polysulphide requisite for soluble sulphur compounds rendering the lye impure; introducing ammonium-polysulphide into the lye so as to precipita'tethe nickel contained in the same in the form'of a dissolved nickel cyanogen complex salt, and finally, conducting the sulphide of nickel so obtained back into the washing process.

' 4. The process of separating hydrocyanic acid in the form of ammoniuin-thio-cyanate' from gases containing said acid, ammonia and sulphuretted hydrogen with the aid, of washing lyes containing nickel compounds, said process consisting in adding to the washing lye an amount of the nickel compounds sufficient to produce the 2,008,253 7 amount rammomum-poiysuiphide requisite for the conversion of the hydrocyanic acid into am:

monium-thiocyanate'; and insufficient to) form soluble sulphur compounds rendering the lye impure; introducing ammonium p olysulphide into a part'of the washing lyeduring the washing operationso as'to' precipitate the nickel contained in thesame'in the form of a dissolved nickel cyanogen complex salt, and finally, conducting the liquid'containing suspended sulphide of nickel back into the washing process. 5. The process of separating hydrocyanic acid in the form of ammonium thio 'cyanate from gases containing saidlacid; ammonia, and sin- .phuretted hydrogen with theaid of washing hles containing nickelcompounds said process 0on sistingin adding to the washing lye an amount of the nickel compounds suflicient to produce the V amountoi ammonium-polysulphide requisite for the conversionof the hydrocyanic acidinto ainmonium-thiocyanate, and insufficientl to form soluble sulphur compounds rendering thelye impure; introducing ammoniumpolysulphide into the entire'amount of the w'ashing lye and after the saturation of said lye with aminohium"thio- 'cyanatelia's become a maximum'soias to precipi tate the nickel contained in the same in theform of a dissolved nickel cyanogen coniplexsalt, and finally, conducting the separated sulphide of nickel so obtained'back into the washing process.

6. The process of separating hydrocyanic acid in -the form of ammonium thio-cyanate from gases containing said acid, ammonia, and sulphuretted hydrogen with the aid or washing lyes containing nickel compounds, said process consistinginadding'to thewashing lye an amount of the nickel compounds sufiicient to produce the amount of ammonium-polysulphide requisite for the conversion of the hydrocyanic acid into ammonium-thiocyanate, 1 and insuificient to form soluble sulphur compounds rendering the lyeimpure, treating the liquid leavingthe "washing circuitand containing still suspended nickel sulphide and dissolved nickel cyanate 'cornplex'salt with air so as to produce thereby the sulphur necessary fortheiormation of ammoniumpolysulphide to precipitate said nickel cyanogen complex salt inf the iorm of sulphide oinickel, and conducting'said liquidthereafter back into the washing process. J

Y 7. The process'of separating hydrooyanic acid 'in the form of ammonium "thio-cyanate from gases containing; said acid, ammonia, and sul-' phurette'd hydrogen with the aid of washing lyes containing nickel compounds, said process consisting in adding to'the washing lye an amount of the nickelcompounds sufii'cient to produce the amount of ammonium-polysulphide requisite for the conversion of the hydrocyanic acid intoaminonium-thioqianate,said addition of "the nickel compounds being, besides, chosen so -small that the hydrocyanic acid is'not completely washed out, and adding, finally, puli e'rulent sulphur'so as to render the further washing-out quantitative.

l r WALTER'KLEMPT. 

